Compared effects of enflurane and of halothane on the intracranial pressure and the cerebral perfusion pressure in the dog.

In this study, we compare the values of the systemic arterial pressure (S.A.P.), of the intracranial pressure (I.C.P.) and of the cerebral perfusion pressure (C.P.P.) -- (C.P.P. = P.A.S. -- I.C.P.) -- in the anesthetized dog, artificially ventilated, before and after vaporization with two halogenated anesthetics, enflurane and halothane at different concentrations. The measures were made in a group of ten dogs in normoventilation and intracranial normotension conditions, in one hypercapnic dog with intracranial hypertension, and in four dogs after injection of sodium laurylsulfate in the internal carotide to induce cerebral edema. In normocapnic dogs, enflurane and halothane increase the I.C.P., decrease the S.A.P. and the C.P.P. Under enflurane 0.5%, the I.C.P., the S.A.P., and the C.P.P. show no significant variations. The increase in I.C.P. is due to the cerebral vasodilator effect of the anesthetics. At equal concentrations, halothane is more hypotensive than enflurane, and the changes in C.P.P. induced by both anesthetics depend more on the variations in S.A.P. than on the variations in I.C.P. In the hypercapnic dog, the vaporization of enflurane and of halothane further enhance the increase in I.C.P., since the vasodilator effect of the anesthetics is added to that of hypercapnia. The S.A.P. and the C.P.P. drop in relation to the concentrations of vaporization used. After sodium laurylsulfate, the administration of enflurane and halothane is accompanied by a drop in S.A.P. and in C.P.P. In this group, the decrease in I.C.P. recorded in two thirds of the cases can be explained by the hypotensive effect of the anesthetics which decreased the hydrostatic pressure in the cerebral vascular bed, a maintenance element of the edema.